Modern electricity meters are so-called “smart” electronic meters that are naturally suitable for measuring a quantity of electrical energy supplied by a supplier to an electrical installation via a supply network, and which are also capable of performing a certain number of additional functions: managing tariffs on receiving orders; remote reading and programming; remote client information; etc.
Such electricity meters sometimes include a cutoff member that is connected in a live conductor and that makes it possible to act remotely to cause the electrical installation to be selectively connected to or disconnected from the supply network.
The electric current flowing through the cutoff member in such an electricity meter naturally tends to raise the temperature inside the electricity meter. Nevertheless, certain faults that can occur in the electricity meter can lead to abnormal heating of the cutoff member and to an abnormal rise of temperature inside the electricity meter. The abnormal rise of temperature runs the risk of damaging the electricity meter, or even of leading to a fire in the electrical installation starting from the electricity meter.
Document WO-A-2010/149921 proposes detecting abnormal heating of the cutoff member that might lead to such an abnormal temperature rise inside an electricity meter. In that document, the heating comes from an abnormal increase in the internal resistance of the cutoff member as a result of degradation of the surface state of poles of the cutoff member. That document teaches estimating the abnormal increase in the internal resistance by measuring a voltage across the terminals of the internal resistance.
Nevertheless, it should be observed that the internal resistance of a cutoff member is very low, being of the order of 500 microohms (μΩ). The internal resistance of the cutoff member may for example double in the event of contact blackening, so as to reach 1 milliohm (mΩ). When an electric current of 10 amps (A) passes through the closed cutoff member, the potential difference across the terminals of the cutoff member goes from 5 millivolts (mV) to 10 mV. It is therefore necessary to be capable of measuring a potential difference of 5 mV, which represents very high metrological precision (the necessary precision is 0.02%, assuming that a voltage sensor used for performing this measurement is also to be capable of measuring the voltage supplied by the mains, i.e. 230 volts (V)). That method is also extremely sensitive to noise. The voltage sensor used must therefore be of very high performance and thus very expensive.
It should also be observed that Document WO-A-2010/149921 is capable only of detecting a temperature rise due to a fault in the cutoff member, and not due to some other cause, e.g. such as a problem of connecting an electric cable to the electricity meter.